Chad Huard » Featured

Switch Bounce

Chad — Tue, 13 Apr 2010 00:26:19 +0000

Most people who have dabbled in embedded design know that all mechanical switches have some amount of “bounce” where they are not making solid contact for a short time after being pressed or released. If you manage to read the button fast enough that you make more than one reading while the button is still bouncing you can get erroneous readings. I was working on a lab for my microcomputer class that used a flip-flop to de-bounce the rising edge of the button press, but I was still getting extra button press readings when I was releasing the button. This was obviously a job for scopezilla. What I found was interesting:

: The Culprit!

: Rising Edge

: Falling Edge

So, the big problem? Well, it turns out that the glitch that can be seen in the falling edge image was really the problem, not bouncing on the rising edge. It didn’t occur every time I pressed and released the button, but frequently enough to be a real pain (perhaps 10%). All of the de-bouncing in the world on the leading edge could not keep the processor from interpreting the high after the glitch as a second button press. Obviously more sophisticated de-bouncing is required.

Introducing Scopezilla: HP 54720A

Chad — Mon, 12 Apr 2010 23:42:03 +0000

I decided that I needed a scope for my projects a few weeks ago. After searching for a little while I decided on a used HP 54720A. This thing is a monster! It is about the size of tall kitchen trash-can and weighs a whopping 75lbs. For all that massiveness you get 1.1GHz bandwidth, 4GS/s (thats four Billion… with a B, samples per second folks) and 32kS record length! I have been playing around with it for a few days now and I can say that it is fairly easy to use and provides incredible resolution and detail. I will take a few pictures of it for posterity when I finally move it upstairs (right now it is on the dining table… a setup that my wife just barely tolerates, bless her heart) until then you I will just post some screen captures.

Regulated Power Supply Noise

Monitoring Event Timing on HC11 Board

HC11 EVB E-clock (top) and A0 Address Bus Pin (bottom)

Equate File for HC11 Registers

Chad — Wed, 31 Mar 2010 14:51:54 +0000

I couldn’t find an equate file of the registers for the 68HC11 anywhere online, so I just typed it all in myself. To spare others from the same tedium I am posting it here in hopes that anyone who needs it can find it easily. The file includes both the extended addresses of each of the HC11 registers, but also the offsets from $1000 for use with indexed addressing. To use it, just put the file in the same folder as your program and insert the following code at the top of your assembly program and you will be able to call all of the registers by name:
#include "EQU.txt"

Hopefully you find it useful.

EQU.txt

Lab 2 – Quantitative Metallography

Chad — Fri, 05 Mar 2010 00:02:37 +0000

Quantitative metallography is the study of metallic crystal structures from the perspective of numeric quantities. Examples of quantitative metallographic measurements include number of grains per unit area and fraction of specific phase per unit volume. These two quantities are what we will investigate in this lab.

Download (PDF, 1.39MB)

Lab 6 – Creep

Chad — Thu, 04 Mar 2010 01:45:08 +0000

Creep is a condition where a material will undergo progressive plastic deformation under constant load or stress. In most metals, this behavior is only present at elevated temperatures, but a few soft metals like tin and lead will experience creep at room temperatures. This experiment will explore the creep behavior of lead.

Download (PDF, 369.37KB)

Distortion Testing

Chad — Sun, 24 May 2009 22:35:24 +0000

I have been doing a few distortion measurements of the drivers in my current project. I have become concerned about the distortion products of the mic itself. The following is a test of the distortion of my HDS Nomex driver driven at 2.83V with mic distances of 4″, 8″ & 16″. The distortion products should be the same % in each, any increase can be directly attributed to the mic.

Click on any image above and use keyboard arrow keys to quickly compare images.

As you can see, the 3rd harmonic doesn’t change apreciably. The 2nd on the other hand increases dramatically with each doubling of the SPL.

Peerless/Usher – Post #5

Chad — Fri, 15 May 2009 21:33:47 +0000

Another Crossover

This one has a little more informed crossover point. I ended up with 1800Hz LR4. Hopefully this will be low enough to attenuate the peak in 3rd harmonic on the woofer (centered @ 1600) as well as get rid of most of the weird peak in high order harmonics in the tweeter around 2k. The impedance looks ok, only dropping to 4 ohm min in the 3k-4k region. Listening to one speaker with the crossover emulator built into soundeasy this crossover sounds pretty good.